Sampled digital audio data, from sources such as speech or musical instruments, particularly in the form of linear Pulse Code Modulation (PCM) samples, tends to include a high degree of redundancy because of the high degree of dependence between successive sample values.
With the proliferation of multimedia applications, several compression/decompression algorithms have been promoted. U.S. Pat. No. 4,396,906 to Weaver describes a system which includes means for digitizing analog signals, for compression filtering the digital samples, and for Huffman encoding the compressed digital samples for recording or transmission. The U.S. Pat. No. 4,396,906 patent also describes a receiving system which includes a Huffman decoder, a digital reconstruction filter and means for converting the decoded, reconstructed digital signals back to analog form. A similar system is describe in an article by U. E. Ruttimann et al., entitled "Compression of the ECG by Prediction or Interpolation and Entropy Encoding", IEEE Transactions on Biomedical Engineering, Vol. BME-26, No. 11, November 1979, pp. 613-623. Another system is described in an article by K. L. Ripley et al., entitled "A Computer System for Capturing Electrocardiographic Data", Pro. Comput. Cardiol., 1976, pp. 439-445.
To achieve constant compression rates, however, existing schemes have sacrificed audio integrity, losing some of the information contained in the original audio signal. There are lossless compression algorithms which have been used to compress text and data files with completely accurate recovery of the primary data upon decompression. These techniques, however, are optimized for text and data and are only marginally effective in compressing audio data.
Some methods of audio compression are based on psychoacoustics. Such perceptual coding algorithms drop psychoacoustically imperceptible audio information. While acceptable for most consumer audio delivery formats, such as MiniDisc, DAT and CD-ROMs, such an approach is inadequate for professional audio production, where material may go through multiple iterations of compression and decompression before being mastered onto the final delivery medium. Any loss of audio information is compounded with each iteration causing a serious compromise in the audio integrity of the finished product. There clearly exists a need for a truly lossless, realtime compression technology.